The Fillers Improve Of Bioretention System And Experiment Study On Phosphorus Purification

With the acceleration of urbanization,the problem of eutrophication of receiving water caused by rainwater is increasingly prominent.Phosphorus is considered to be the main limiting element of water eutrophication.Bioretention technology is considered one of the most effective stormwater control measure.Based on the actual situation of Feng Xi new city in Xi’an,the effective phosphorus removal filler was studied in this paper,so as to provide a basis for the practical promotion of bioretention technology.In this paper,a variety of single fillers were first selected,their physicochemical properties and adsorption performance were measured,and several phosphorus removal modifiers were selected;mixing the modifier and BSM,the effect of modifier addition ratio on the adsorption performance of modified fillers was determined by static adsorption experiments;the adsorption capacity of the modified fillers were studied by dynamic adsorption experiment.phosphorous removal capacity and main influencing factors of bioretention fillers under different working conditions were studied by pilot plant;two raingardens with different filler types and structures were monitored,and the effect on water quality and water quantity of actual rainwater was analyzed.The main conclusions are as follows:(1)Comprehensive evaluation of physicochem ical properties,adsorption performance,and price of a single filler,and preparation of BSM based on research at home and abroad.The BSM ratio:30%soil.+65%sand+5%wood chips(by mass).In the fillers,4 kinds of phosphorus removal modifiers with good adsorption effect and lower price of WTR,fly ash,green zeolite,and maifanite were studied,The 4 modifiers were added to BSM at different mass ratios(5%,10%,and 15%)for isothermal adsorption experiment and the theoretical saturated adsorption amount was used as an evaluation index.The results show that the filler adsorption effect is better when WTR and fly ash are used as modifiers,and the saturated adsorption amount also increases with the increase of the addition ratio.The addition of maifanite and green zeolite has a smaller increase in the adsorption performance of the filler.(2)In the dynamic adsorption experiment of 6 kinds of fillers,the modified fillers added with 10%of fly ash,green zeolite,and maifanite appeared saturated when the influent amount was approximately equivalent to 5 years of total rainfall,and the adsorption amount was 22～30 mg/kg.The soil was saturated when the influent amount was about 11 years of total rainfall,and the adsorption amount was about 59.44 mg/kg;the modified filler added with 10%WTR did not reach saturation by the amount of water equivalent to 15 years of rainfall,and the adsorption amount was about 94.29 mg/kg.The desorption process of soil,BSM,added 10%maifanite,10%fly ash,10%WTR,10%green zeolite modified fillers desorption rate were 20.03%,26.42%,26.85%,47.15%,7.62%and24.53%,and the final amount of equilibrium adsorption of the mixed filler added to WTR was the largest.(3)The filler infiltration rate had a great influence on the peak flow rate reduction and lag time.As the decrease of infiltration rate,the lag time is relatively longed,and the peak flow rate reduction is relatively increased.The reduction rates of bioswales were between 30%and 40%averagely,in which difference is relatively small.Under the same kind of fillers,the water quantity reduction rates were decreased with the height of the basin.The same kind of fillers wether hierarchical or hybrid structure had little effect on the effect of water reduction.The type of fillers had great influence on the removal of phosphorus concentration and the effect of load reduction.On the whole,the filler added WTR as a modified mixture is optimal for phosphorus removal.(4)The consequence of the on-site monitoring of the bioretention shows that the effect of raingarden on water volume reduction is obvious.It had a certain adsorption effect on positive phosphorus to set up the submerged zone and add WTR as modifer of the phosphorus removal,which is obviously superior to the traditional loess filler raingarden.In total nitrogen and nitrate nitrogen removal,although the removal rate is low,there is not a lot of leaching in the stable period,and the effect is better than the traditional garden structure.